Nick Finnis, a forecaster at netweather.tv, said there would also be heavy rain in southern Scotland.

The rest of the country should see sunny spells but also heavy and thundery downpours, with temperatures of 18C (64F) in London and 15C (59F) in Cardiff and Glasgow.

‘It looks like we will continue to see further cloud and persistent rain affecting northern, central and eastern England, southern and eastern Scotland through much of the day on Wednesday and into Thursday too, accompanied by a cool north-easterly wind,’ Mr Finnis said.

He predicted the rain would bring a ‘continued risk of localised flooding’ but said this should ease late on Thursday, while there would be a mix of sunshine and showers elsewhere.

‘It will be generally on the cool side everywhere,’ Mr Finnis added. Friday is expected to be drier and brighter but there is still a risk of isolated showers in some places.

The predicted heatwave will not get going until later in the year.

But experts claim there is a 75 per cent chance that sizzling temperatures in July and August will make 2014 the hottest summer on record.

The El Niño weather pattern will fuel the trend, according to a report by researchers from the Justus Liebig University in Giessen, Germany, published in the journal PNAS.